1. Field of the Invention
This present invention relates to an electrochemical method and apparatus for the synthesis of ammonia.
2. Background to the Related Art
Ammonia (NH3) is a colorless alkaline gas that is lighter than air and possesses a unique, penetrating odor. Since nitrogen is an essential element to plant growth, the value of nitrogen compounds as an ingredient of mineral fertilizers, was recognized as early as 1840. Until the early 1900's, the nitrogen source in farm soils was entirely derived from natural sources. Haber and Bosch pioneered the synthesis of ammonia directly from hydrogen and nitrogen on a commercial scale in 1913. Further developments in large-scale ammonia production for fertilizers have made a significant impact on increasing the world's food supply.
Virtually every nitrogen atom of a nitrogen compound travels from the atmosphere to its destined chemical combination by way of ammonia. Industrial uses of ammonia as a nitrogen source has recently consumed a greater share of the total ammonia production, accounting for 20% of the world output. Up to 80% of the ammonia produced is used for the production of nitrogen-based fertilizers, accounting for about 3% of the world's energy consumption. In many developing countries, the capability for ammonia synthesis is the first sign of budding industrialization. In the United States last year there was over 19 billion tons of ammonia produced.
Many methods of ammonia synthesis have been investigated. These methods include the catalytic synthesis of ammonia from its elements using large-scale pressures and temperatures, indirect ammonia synthesis using the steam decomposition of nitrogen based compounds, and the formation of ammonia with the aid of electrical discharge. Only recently has the possibility of using electrochemistry for ammonia synthesis been demonstrated. The electrochemical process is operated at atmospheric pressure and 570° C., which is a similar temperature to that used in the Haber-Bosch process. The apparatus consists of a non-porous, strontia-ceria-ytterbia (SCY) perovskite ceramic tube closed at one end and then further enclosed in a ceramic tube. Electrodes, made from polycrystalline palladium films, are deposited on the inner and outer walls of the SCY tube.
Ammonia gas is passed through the system, where the amount of decomposition due to heating can be measured. Subsequently, gaseous hydrogen is passed through the quartz tube and over the anode surface, where the hydrogen is converted to protons:3H2→6H++6e−  (1) 
The protons then diffuse through the solid perovskite electrolyte to the cathode surface, where they come in contact with the nitrogen gas and the following reaction takes place:N2+6H++6e−→2NH3  (2) However, the efficiency of the reaction is reduced by the high temperatures needed for the reaction to occur.
Therefore, there remains a need for an improved method of producing ammonia. It would be desirable if the improved method could produce ammonia at lower temperatures and lower pressures, while achieving a greater conversion than existing methods. It would be even further desirable if the improved method were compatible with existing process units, such as being able to use the same hydrogen and nitrogen sources as are used in the Haber-Bosch process.